Electromechanical cables are used in oil and gas well logging and other industrial applications. Electromechanical cables provide an electrical power supply for down-hole instruments that record and sometimes transmit information to the surface (“Instrument Power”). Instrument power is usually steady-state, meaning that the power levels are substantially constant during a logging run. Some logging tools, however, also require additional and simultaneous power to operate transmitters (“Auxiliary Power”). The Auxiliary Power may also be used to operate down-hole motors on an intermittent basis. One example is calipers that are operated by a user on the surface or automatically by the logging system that are intermittently operated to obtain measurements or samples of the properties of a bore-hole.
The amount of electric current transmitted through the electromechanical cable that is actually received by the down-hole tools is dependent upon many factors, including the conductivity of the material, the electrical resistance of the material, and the cross-sectional area of the conductive material. Often, an electromechanical cable loses electrical energy through heat dissipation generated by the resistive effect of the copper conductors. It is common that in order to deliver a power “P” to the down-hole tools, a power of 2P must be input into the system because P power is lost due to dissipation of heat due to resistance of the conductor over the entire length of the conductor. The generation of resistive heat poses a problem and significantly limits the amount of current fed through the electromechanical cable, particularly when the electromechanical cable is stored on a drum during use. When the excess electromechanical cable is stored on a drum during operation, the heat has little ability to dissipate into the atmosphere or surrounding environment due to the fact that many layers of cable may be overlapped and the heat has an additive effect. Therefore, care must be taken to avoid over heating the cable because the conductor may short-circuit or otherwise become dangerous if the internal temperature of the cable rises above a temperature that softens or melts the insulating polymer layer surrounding the wire. It is often the heat build up during storage on the drum during operation that limits the amount of power that can be delivered by an electromechanical cable to the down-hole tools. For example, a 7/16″ diameter cable may usually withstand ¼ to ⅓ of a watt per foot of power dissipation without overheating. This limits the power input into the cable to that which will not cause over the ¼ to ⅓ watt per foot power dissipation. The loss of energy resulting from heat dissipation due to the resistance of the conductor is undesirable especially in applications where the cable is being used for periods of longer than several minutes at a time.
Therefore, there is a need in the art to reduce the resistance of a conductor in order to allow more power to be transferred through it while reducing or maintaining the same or less heat generation. One way to reduce the resistance and increase the power is to increase the diameter of the conductor. However, this necessarily increases the weight of the cable thereby introducing additional weight that (1) the cable itself must support and/or (2) requiring adjustment of the existing trucks in order to convey, transport, and utilize the larger diameter cable. Further, because of the increase in horizontal drilling in the industry, the length of bore holes has become longer, requiring longer lengths of electromechanical cable to supply power, the horizontal drilling necessitates the use of certain “tractor” devices to push or pull tools inside the wellbore. The tractors must pull the length of the electromechanical cable in the horizontal portion of the well as well as the other tools through the bore hole and, therefore, there is also a need in the art to reduce the weight of the electromechanical cable in addition to decreasing the resistance of the copper conductor. A lighter weight cable will also contribute to making logging of oil and gas wells more efficient by saving energy demanded by the down-hole tools themselves because more energy is required to power the tractor when it must move a heavier cable
Thus, there is a substantial need in the art for an electromechanical cable having (1) a lower electrical resistance that efficiently delivers power to down-hole tools, and (2) is lighter weight than conventional electromechanical cables.